This invention relates to a method and apparatus for presetting a receiver and more particularly to a method and apparatus for presetting a receiver wherein the oscillation frequency of a local oscillator is set by means of a synthesizing system for the purpose of selecting a broadcasting station.
A receiver utilizing a synthesizing system contemplates stable reception of the signal wave by producing a local oscillation from a voltage controlled oscillator in a phase locked loop. In this case, a programmable frequency divider is included in the feed-back loop for the phase locked loop and the result of the comparison of the frequency of the frequency divided signal and a reference frequency is used to control the voltage controlled oscillator so that the accuracy of the local oscillation frequency is determined by the accuracy of the reference frequency. For this reason, it is possible to perform a stable reception by using a crystal oscillator as the source of the reference frequency. Change of the local oscillation frequency, that is the station selection, is made by properly setting the ratio of frequency division of the frequency divider. As a method of setting the ratio of frequency division, so-called automatic tuning method has been proposed wherein an up-down counter is swept with a sweeping pulse and when an output having an intermediate frequency of the received high frequency signal is obtained the counting operation of the up-down counter is stopped and the ratio of frequency division is set. A method of setting the up-down counter by using a manually operated transfer switch has also been used.
Where the automatic tuning is performed by the method of setting just described each time an intermediate frequency output is obtained (or a station is selected) the counting operation of the up-down counter is stopped so that in order to set a desired broadcasting station it is necessary to restart the up-down counter each time it stops. Such station selection operation is of course troublesome. Further, in the case of the manual setting because the frequency of the broadcasting station is different in a particular receiving area the operator is required to be informed beforehand of the frequency of the desired broadcasting station. Such station selection operation is also troublesome.